Bunyaviridal reaper proteins and uses therefore

ABSTRACT

Viral proteins with sequence and functional similarity to the drosophila cell death protein known as Reaper are provided. Reaper plays an important role in the apoptotic pathway. Methods using the viral proteins and nucleotides encoding such proteins are described.

This application is filed pursuant to 35 U.S.C. §371 as a United States National Phase Application of International Application No. PCT/US01/05275 filed Feb. 16, 2001, which claims priority from U.S. Provisional Application No. 60/184,055 filed Feb. 22, 2000.

FIELD OF THE INVENTION

The present invention relates to a viral cell death gene and the protein expressed thereby, and in particular, but not exclusively, to nucleotide sequences, expression vectors, cell lines, antibodies, screening methods, compounds, methods of production and methods of treatment, related to them.

BACKGROUND OF THE INVENTION

Apoptosis is a form of programmed cell death, by which an organism eliminates extraneous or harmful cells. Apoptosis plays a role in normal development and homeostasis, as well as in diseases such as cancer and neurodegenerative diseases.

Apoptosis occurs via the activation of intrinsic cell-suicide programs; activation is regulated by many different signals, both intracellular and extracellular. Various viral and metazoan apoptosis inducer genes have been identified; inhibitors of apoptosis (IAP) proteins have also been identified that act to suppress apoptosis.

At least three apoptotic activator proteins have been identified in Drosophila melanogaster: reaper (rpr), head involution defective (hid) and grim. The N-terminal sequences of these proteins are highly conserved. Avdonin et al., Proc. Natl. Acad. Sci. USA 95:11703 (1998). Proteins that inhibit apoptosis (IAPs) have also been identified in Drosophila. Hay et al., Cell 83:1253 (1995); Wing et al., Cell Death Differ. 5:930 (1998).

The product of the reaper gene is required for programmed cell death in Drosophila. Cell death induced by the reaper protein has been shown to be blocked by the baculovirus p35 protein, a viral product that inactivates proteases. White et al., Science 271:805 (1996).

The Drosophila Grim protein is also an activator of apoptosis, independent of Reaper. Expression of Grim RNA coincides with the onset of programmed cell death during embryonic development, and ectopic induction of grim has been show to trigger extensive apoptosis in transgenic animals and in cell culture. Similar to the Reaper protein, cell killing by grim can be blocked by coexpression of the viral p35 product. The grim gene product has been postulated to function in a parallel cell death signalling regime that activates a common set of downstream apoptotic effectors. Chen et al., Genes Dev. 10:1773-1782 (1996).

Viral infection of host cells, and replication therein, is often associated with inhibition of apoptosis to enable viral replication and the subsequent stimulation apoptosis of the host cells for viral particle release. Certain viral gene products have been shown to specifically inhibit or induce apoptosis. However, many viruses additionally encode proteins that inhibit apoptosis, prolonging the survival of infected cells and thereby aiding viral replication or viral persistence in the host.

SUMMARY OF THE INVENTION

A first aspect of the present invention is a method of screening compounds for the ability to modulate the apoptotic effects of viral reaper proteins on cells. The protein may consist of or comprise an amino acid sequence selected from SEQ ID NOs:2-17.

According to another aspect of the invention there is provided a method of using nucleotide sequences encoding viral reaper proteins or a variant thereof, or a nucleotide sequences which are complementary thereto. Preferably the nucleotide sequence is a cDNA sequence. Particularly preferably the nucleotide sequence is selected from SEQ ID NOs:2-17.

According to another aspect of the invention there is provided a method of treating cells using viral reaper proteins, to affect the cell's apoptotic mechanism.

According to another aspect of the invention, there is provided a method of using expression vectors comprising a nucleic acid sequence as referred to above that is capable of expressing a viral reaper protein.

According to another aspect of the invention there is provided a method of treatment or prophylaxis of a disorder that is responsive to modulation of apoptosis by a viral reaper protein modulator, the method comprising administering to a subject in need thereof an effective amount of a viral reaper protein modulating compound. Preferably the disorder is selected from viral infections in mammalian subjects.

According to a further aspect of the invention there is provided use of a compound that modulates viral reaper protein activity in a method of formulating a medicament for treatment or prophylaxis of a disorder that is responsive to modulation of viral reaper protein activity, in a subject in need of such treatment. Preferably the disorder is selected from viral infections in mammalian subjects.

BRIEF DESCRIPTION OF THE FIGURES

The present invention will be further described by way of example and with reference to the following figures:

FIGS. 1A and 1B show the amino acid sequences of the nonstructural (NSs) viral proteins from fifteen different virus, aligned with the amino acid sequence of the complete Reaper protein (SEQ ID NO: 1) and a portion of the Grim protein from Drosophila melanogaster (SEQ ID NO:18). A majority sequence for the viral reaper protein is provided as SEQ ID NO:2.

FIG. 2 shows Western blot results indicating binding of various reaper proteins to Xenopus scythe protein (Example 4). RPR1 and RPR2 indicate preparations of Drosophila Reaper, SA indicates San Angelo virus reaper, and CE indicates California Encephalitis virus reaper; GST1 and GST2 are preparations of glutathione-S-transferase used as controls.

FIG. 3 graphs the results of a colorimetric assay to detect caspase activation in Xenopus cell-free extracts with added Drosophila reaper (Rpr 4/5, Rpr 12/00, Rpr 12/20), San Angelo virus reaper (SA), and California Encephalitis virus reaper (CE). Glutathione-S-transferase (GST) was used as a control. The Y-axis shows absorbance at 405 nm; the X-axis=time in hours.

DETAILED DESCRIPTION OF THE INVENTION

Viral proteins with sequence similarity to the Drosophila melanogaster Reaper protein have been identified, and shown to be capable of activating caspases in vertebrate cell-based assay. Cellular death by apoptosis is, with only some exceptions, executed by the family of proteases known as caspases. The caspases are synthesized as inactive zymogens and activated during apopototic pathways. (Chinnaiyan and Dixit, Curr. Biol. 6:555 (1996); Muzio et al, J. Biol. Chem. 273:2926 (1998); Yang et al., Mol. Cell. 1:319 (1998); Zou et al., Cell 90:405 (1997)). Caspase activation (and thus ultimately apoptosis) can be blocked by the IAP (inhibitor of apoptosis) proteins and anti-apoptotic members of the Bel-2 family (Adams and Cory Science 281:1322 (1998); Deveraux and Reed, Genes Dev. 13:239 (1999)).

The present viral genes and their expression products provide useful screening assays for the identification and development of novel pharmaceutical agents, including agonists and antagonists of the viral reaper proteins, and compounds able to enhance or inhibit caspase activation and/or cellular apoptosis; such compunds may be used in the treatment and/or prophylaxis of disorders such as cancer and viral infections. In particular, the present methods are useful in identifying compounds that enhance or inhibit apoptosis due to caspase activation.

Accordingly, it is an object of the present invention to provide methods of using isolated viral reaper proteins. Other objects of the present invention will become apparent from the following detailed description thereof.

The present inventors identified viral proteins with sequence similarity to the D. melanogaster Reaper protein. More particularly, the present inventors determined that the non-structural protein (NSs) of viruses of the genus Bunyavirus exhibited sequence similarity to the Drosophila Reaper protein.

Viruses of the genus Bunyavirus (family Bunyaviridae) are single stranded RNA negative-strand viruses that infect vertebrates. There are 18 antigenic groups of the genus Bunyavirus (at least 161 viruses) and several additional ungrouped viruses.

The California encephalitis virus, LaCrosse virus, San Angelo virus, Snowshoe Hare virus, Jerry Slough virus, Jamestown Canyon virus, Keystone Virus, Melao virus, Trivittatus virus, Morro Bay virus, Inkoo virus, Serra do Navio virus, South River virus, Lumbo virus, and Tahyna virus are each members of the genus Bunyavirus. The genome consists of a large (L) RNA, a medium (M) RNA, and a small (S) RNA. The nonstructural protein (NSs protein) of these viruses is encoded by the small (S) RNA, and is induced in virus-infected cells (Fuller and Bishop (1982) J. Virol. 41, 643-648). The NSs protein of each of these viruses was found by the present inventors to have sequence similarity to the Drosophila Reaper protein (FIG. 1).

A nucleotide sequence encoding D. melanogaster Reaper protein is given at GenBank Accession No. L31631; the protein sequence is provided at Acc. No. AAA18983. The amino acid sequence of the Drosophila cell death protein GRIM is provided at GenBank Acc. No. AAC47727.

The nucleotide sequence encoding San Angelo virus (Prototype VR723) nucleocapsid and non-structural proteins is provided at GenBank Accession U47139. The amino acid sequence of San Angelo virus NSs protein is provided at Acc No. AAC5335.

The amino acid sequence of a NSs of the Snowshoe Hare virus is provided at Accession No. P03514; the nucleotide sequence of a small (S) viral RNA species of snowshoe hare virus is provided at Acc. No. J02390. See also Bishop et al., Nucleic Acids Res. 10 (12), 3703-3713 (1982).

The nucleotide sequence of a La Crosse virus small RNA segment is provided at GenBank Accession No. K00108. The amino acid sequence for a La Crosse Virus non structural protein can be found at Accession No. AAA42780.1

The nucleotide sequence for a California Encephalitis virus small RNA segment, including the nucleocapsid and NSs protein genes, is provided at GenBank Accession No U12797; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC54056.1. See also Bowen, M. D., et al. J. Gen. Virol. 76: 559-572 (1995).

The nucleotide sequence encoding Jerry Slough Virus NSs protein is provided at GenBank Accession No. U12798; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC54048.

The nucleotide sequence encoding Jamestown Canyon Virus NSs protein is provided at GenBank Accession No. U12796; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC54044.

The nucleotide sequence encoding Keystone Virus NSs protein is provided at GenBank Accession No. U12801; the amino acid sequence of the viral NSs protein can be found at Acc. No. 54054.

The nucleotide sequence encoding Melao Virus NSs protein is provided at GenBank Accession No. U12802; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAB60560.

The nucleotide sequence encoding Trivittatus Virus NSs protein is provided at GenBank Accession No. U12803; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAB60562.

The nucleotide sequence encoding Morro Bay Virus NSs protein is provided at GenBank Accession No. U31989; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC55125.

The nucleotide sequence encoding Inkoo Virus NSs protein is provided at GenBank Accession No. U47138; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC55333.

The nucleotide sequence encoding Serra do Navio Virus NSs protein is provided at GenBank Accession No. U47140; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC55337.

The nucleotide sequence encoding South River Virus NSs protein is provided at GenBank Accession No. U47141; the amino acid sequence of the viral NSs protein can be found at Acc. No. AAC55339.

The nucleotide sequence encoding Lumbo Virus NSs protein is provided at GenBank Accession No. X73468; the amino acid sequence of the viral NSs protein can be found at Acc. No. CAA51852.

The nucleotide sequence encoding Tahyna Virus NSs protein is provided at GenBank Accession No. Z68497; the amino acid sequence of the viral NSs protein can be found at Acc. No. Z68497.

The present viral Reaper proteins act as apoptotic modulating proteins, affecting apoptosis in host cells. Discovery of these viral proteins provides methods to screen compounds for the ability to block or enhance the viral reaper function, and the use of compounds identified thereby to modulate apoptosis. Apoptosis may also be modulated by the administration of viral reaper proteins (or a functional variant or fragment thereof) to a cell. Administration may utilize isolated nucleic acid molecules encoding the viral reaper proteins, vectors containing such molecules, and host cells transfected with the same. The host cells may be any cell suitable for cultivation of the virus, as is known in the art. More preferred are vertebrate cells, including mammalian cells.

The present proteins (and functional variants and fragments thereof) and nucleotides expressing the same, are useful in several settings. Where a virus is being cultivated, either in cell culture or in vivo, the presently identified viral reaper proteins (and/or the compounds discovered in the screening assays described above) may be used to modulate apoptosis of infected host cells, by administering the protein or compounds to the cells. Inhibiting apoptosis of the host cell is useful where further replication of the virus within the host cell can be attained and is desirable. Inducing apoptosis of the host cell is useful where infection of additional cells is desirable, in harvesting virus, or where it is necessary and desirable to terminate survival of the host cell in order to halt further viral replication/propagation.

Additionally, the present proteins and/or compounds discovered using the present screening assays, may be used in the treatment of certain conditions involving aberrant apoptosis of a subject's cells. Viral reaper proteins and/or such compounds may be administered to a preselected population of cells in a subject, to modulate apoptosis of those cells. Such a method is useful in conditions where the normal apoptotic mechanism of the subject's cells is altered, e.g., in cancer and neoplastic growths. Such a method is also useful in treating viral infections.

The present invention also provides a method to screen compounds for the ability to inhibit or enhance the function of the viral reaper proteins (e.g., to act as antagonists or agonists of the viral reaper protein function). Such compounds will be useful in the above-described methods. Such compounds may be administered alone, to act upon endogenous viral reaper proteins produced within an infected host cell; or they may be administered to a cell in conjunction with exogenous viral reaper protein where needed (e.g., where the compound enhances the effects of the exogenous viral reaper protein).

As used herein, “sequence similarity” of proteins refers to the similarity of the amino acid sequence between two proteins. Various computer programs are commercially available that determine sequence similarity, and are known to those skilled in the art. The degree of sequence similarity takes into consideration both amino acid residues that are identical, as well as those that are conservative amino acid substitutions (as is known in the art).

“Sequence similarity” as used in the present specification and claims refers to DNA sequences, (or RNA sequences; or amino acid sequences) that have only slight and non-consequential sequence variations between them. In this regard, ‘slight and non-consequential sequence variations’ mean that the sequences will be functionally equivalent. Functionally equivalent sequences will function in substantially the same manner to produce substantially the same results.

As used herein, two amino acid sequence that have substantial “sequence similarity” are those having at least about 50% or 55% sequence similarity, and preferably at least about 60%, 65%, 70%, 75%, 80%, 85%, or even about 90% or 95% similarity. Changes in the amino acid sequence of peptides can be guided by known similarities among amino acids and other molecules or substituents in physical features such as charge density, hydrophobicity, hydrophilicity, size and configuration, etc. For example, the amino acid Thr may be replaced by Ser and vice versa, and Leu may be replaced by Ile and vice versa.

The peptides of the present invention include not only natural amino acid sequences, but also peptides which are analogs, chemical derivatives, or salts thereof. The term “analog” or “conservative variation” refers to any polypeptide having a substantially identical amino acid sequence to the peptides identified herein, and in which one or more amino acids have been substituted with chemically similar amino acids. For example, a polar amino acid such as glycine or serine may be substituted for another polar amino acid; a basic amino acid may be substituted for another basic amino acid, or an acidic amino acid may be substituted for another acidic amino acid; or a non-polar amino acid may be substituted for another non-polar amino acid. There term “analog” or “conservative variation” as used herein also refers to a peptide which has had one or more amino acids deleted or added to a polypeptide of the present invention, but which retains a substantial sequence similarity (at least about 85% sequence similarity, and preferably at least 90%, 95%, 98% or even 99% sequence similarity), where the peptide retains the viral reaper protein function or generates an antagonistic viral reaper function.

Given the amino acid sequence of a particular viral protein, a nucleotide sequence encoding the protein can be readily determined, and a nucleotide molecule encoding the protein can be prepared.

The present invention also encompasses the use of nucleotide molecules that encode viral reaper proteins. Examples of such nucleotide sequences are below. Due to the degeneracy of the genetic code, one skilled in the art will be able to readily devise alternative nucleotide sequences that encode a given protein, where the amino acid sequence of the protein is known.

nucleotide sequence encoding Drosophila melanogaster Reaper Protein L31631 (SEQ ID NO:19) atggcagtgg cattctacat acccgatcag gcgactctgt tgcgggaggc ggagcagaag 60 gagcagcaga ttctccgctt gcgggagtca cagtggagat tcctggccac cgtcgtcctg 120 gaaaccctgc gccagtacac ttcatgtcat ccgaagaccg gaagaaagtc cggcaaatat 180 cgcaagccat cgcaatga nucleotide sequence encoding San Angelo Virus NSs protein U47139 (SEQ ID NO:20) atgatgtcgc atcaaccggt gcaaatggat ttgatcctga tgcagggtat ctggcattct 60 gtgttaaaca tggggagtcg atcagtttgt cttcagttag gatcttcttc ctcaatgccg 120 caaaagccaa agctgctctc tcgcgtaaac cagagaggaa agcaaatcct aaatttggcg 180 agtggcaggt ggagattgtc aataatcatt ttcctggaaa caggaacaat ccaattgaca 240 acctcgatct taccatccac agattgtctg gatacctggc tagatgggtt ctag 294 nucleotide sequence encoding Snowshoe Hare Virus UP03514 (SEQ ID NO:21) atgatgtcgc atcaacaggt gcaaatggat ttgatcctga tgcagggtat atggcattct 60 gtgttaaata tgcagaatca gtcaatcttg ctgcagttag gatcttcttc ctcaatgccg 120 caaaggccaa ggctgctctc tcgcgtaagc cagagaggaa ggcaaatcct aaatttggag 180 agtggcaggt ggaggttgtc aataatcatt ttcctggaaa caggaacaat ccaattaaca 240 gcgacgatct taccatccac agattgtcag gatatttag nucleotide sequence encoding LaCrosse Virus NSs protein K00108 (SEQ ID NO:22) atgatgtcgc atcaacaggt gcaaatggat ttgatcctga tgcagggtat atggacttct 60 gtgttaaaaa tgcagaatca ctcaaccttg ctgcagttag gatcttcttc ctcaatgctg 120 caaaggccaa ggctgctctc tcgcgtaagc cagagaggaa ggctaaccct aaatttggag 180 agtggcaggt ggaggttatc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccac agattatctg ggtatttag nucleotide sequence encoding California encephalitis NSs protein U12797 (SEQ ID NO:23) atgatgtcgc atccacaggt gcaaatggat ttgatcctga tgcagggtat gtggacttct 60 gtgctaaaca tggggaatca attaaccttg ctgcagttag gatcttcttc ctcaatgccg 120 caaaggccaa ggctgctctc tcgcgtaagc cagagaggaa agctaatcct aaatttggcg 180 agtggcaggt ggaggttgtc aataatcatt ttccagcaaa caggaacaat ccaattggta 240 acaacgatct taccatccac cgcatctcag gataccttgc cagatgggtc ctag 294 nucleotide sequence encoding Jerry slough virus NSs protein U12798 (SEQ ID NO:24) atgatgtcgc atccacaggt gcaaatggat ttgatccaga tgcagggttt gtggcattta 60 tggctgacca cggagagtct atcaatctgt cagccgttag gatcttcttc cttaatgcag 120 caaaagccaa agctgctctc gctcgtaaac cggagcggaa agctactcct aagtttggag 180 agtggcaggt ggagatcatc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccat aggctttcag gatatctag 279 Nucleotide sequence encoding Jamestown Canyon virus NSs protein U12796 (SEQ ID NO:25) atgatgtcgc atccacaggt gcaaatgqat ttgatccaqa tgcagggttt gtggcattta 60 tggctgacca cggagagtct atcaatctgt cagccgttag gatcttcttc cttaatgcag 120 caaaagccaa agctgctctc gctcgtaaac cggagcggaa agctactcct aagtttggag 180 agtggcaggt ggagatcgtc aataatcatt tttctggaaa caggaacaac ccaattggta 240 acaacqatct taccatccat aggctttcag gatatctag 279 Nucleotide sequence encoding Keystone Virus NSs protein U12801 (SEQ ID NO:26) atgatgtcgc atccacaggt gcaaatggat ttgatcctga tgcagggtat gtggcattta 60 tggctaacca tggggagtcg atcagtctgt caaccgttag gatcttcttc cttaatgccg 120 caaaagccaa agctgctctc actcgtaagc cggagcggaa ggctacacct aagtttggag 180 agtggcaggt ggagatcgtc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccttgcac cggatttcag gatatctag 279 Nucleotide sequence encoding Melao Virus NSs protein U12802 (SEQ ID NO:27) atgatgtcgc atcaacaggt gcaaatggat ttgatccaga tgcagggtat ctggcattta 60 caattgcgca tggggaagct atcaatttgt cagccgttag gatcttcttc cttaatgccg 120 caaaagccaa agctgctctc tctcgtaaac cggagaggaa agctactcct aaatttggag 180 actggcaggt ggaaattgtc aacaatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccat cggctttcag gatatcttgc cagatgggtg ctag 294 Nucleotide sequence encoding Trivittatus Virus NSs protein U12803 (SEQ ID NO:28) atgatgctcc atcaacaggt gcaaacggat ttgatcccga tgcagggtat gtggcattta 60 ttgctgcaca tgccggatcg tacgatcttt ctgctgttag gatcttcttc ctcaatgctg 120 ccaaggccaa gaatgctctc tcgagaaaac cagaggggaa ggttagtatt aaatttggcg 180 agtggtcggt ggaggtggtc aataatcatt ttcctggcaa caggaacaat ccaattggta 240 acaacgatct taccatccac agaatttcag gctatctcgc aagatgggtt ctag 294 Nucleotide sequence encoding Morro Bay Virus NSs protein U31989 (SEQ ID NO:29) atgatgtcgc atccacaggt gcaaatggat ttgatcctga tgcagggtat gtggacttct 60 gtgctaaaca tggggaatcg attaaccttg ctgcagttag gatcttcttc ctcaatgccg 120 caaaagccaa ggctgctctc tcgcgtaagc cagagaggaa agctaatcct aaatttggcg 180 agtggcaggt ggagattgtc aataatcatt ttccagcaaa caggaacaat ccaattggta 240 acaacgatct taccatccac cgcatctcag gataccttgc cagatgggtc ctag 294 Nucleotide sequence encoding Inkoo Virus NSs protein U47138 (SEQ ID NO:30) atgatgtcgc atccacaggt gcaaatggat ttgatccaga tgcagggttt gtggcattta 60 tggctgacca tggagaatct attaatttgg cagccgttag gatcttcttc cttaatgcag 120 caaaagccaa agctgctctc gctcgtaaac cggagcggaa agctactcct aaatttggag 180 agtggcaggt ggagattgtc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccac cggctttctg gatacttag 279 Nucleotide sequence encoding Serra do Navio Virus NSs protein U47140 (SEQ ID NO:31) atgatgtcgc atcaaccggt gcaaatggat ttgatccaga tgcagggttt gtggcattta 60 tggctggtca tggggagtcg atcaatctta cagccgttag aatcttcttc cttaatgccg 120 caaaagccaa agctgctctc tctcgcaagc cggagaggaa agctactcct aagtttggag 180 actggcaggt ggagattgtc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccac agaatttcag gatatttag 279 Nucleotide sequence encoding South River Virus NSs protein U47141 (SEQ ID NO:32) atgatgtcgc atccacaggt gcaaatggat ttgatccaga tgcagggttt gtggcattta 60 tggctgacca tggagaatct atcaatctgt cagccgttag gatcttcttc cttaatgcag 120 caaaagccaa agctgctctc gctcgtaaac cggagcggaa ggctaatcct aaatttggag 180 agtggcaggt ggagattgtc aataatcatt ttcctggaaa caggaacaac ccaattggta 240 acaacgatct taccatccac cggctttctg gatatttag 279 Nucleotide sequence encoding Lumbo Virus NSs protein X73468 (SEQ ID NO:33) atgatgtcgc atccaccggt gcaaatggat ttgatcctga tgcagggtat gtggactttt 60 gtgttaaaca tggagaatca atcaatctcc attccgttag gatctttttc cttaatgccg 120 ctaaggccaa ggctgctctc gctcgtaagc cggagaggaa ggctagtcct aaatttggag 180 agtggcaggt ggagatcgtc aataatcatt ttcctggaaa caggaacaac ccaattgata 240 acaacgatct taccatccac cggctgtcag ggtatctggc tagatgggtg ttag 294 Nucleotide sequence encoding Tahyna Virus NSs protein Z68497 (SEQ ID NO:34) atgatgtcgc atccaccggt gcaaatggat ttgatcctga tgcagggtat gtggacttct 60 gtattaaaca tggggaagca attaatctcc attccgttag gatcttcttc cttaatgccg 120 caaaagccaa agctgctctc gctcgtaagc cggagaggaa ggctagtcct aaatttggag 180 agtggcaggt ggaggtcgtc aattatcatt ttcctggaaa caggaacaac ccaattgata 240 acaacgatct taccatccac cggctgtacg ggtatttggc tagatgggtg ctag 294

Nucleotide sequences that have substantial sequence similarity to the nucleotide sequences disclosed herein, and that encode functional viral reaper proteins, are suitable for use in the methods of the present invention.

Thus, use of nucleotides that hybridize to nucleotide molecules encoding the viral reaper proteins of SEQ ID NOs:2-17 are also an aspect of this invention. Conditions which will permit other nucleotide molecules encoding viral reaper proteins to hybridize to the nucleotide sequences disclosed herein can be determined in accordance with known techniques. For example, hybridization of such sequences may be carried out under conditions of reduced stringency, medium stringency, or even high stringency conditions (e.g., conditions represented by a wash stringency of 35-40% formamide with 5× Denhardt's solution, 0.5% SDS and 1×SSPE at 37° C.; conditions represented by a wash stringency of 40-45% formamide with 5× Denhardt's solution, 0.5% SDS, and 1×SSPE at 42° C.; and conditions represented by a wash stringency of 50% formamide with 5× Denhardt's solution, 0.5% SDS and 1×SSPE at 42° C., respectively, to a nucleotide molecule encoding a viral reaper protein as disclosed herein in a standard hybridization assay. See J. Sambrook et al., Molecular Cloning: A Laboratory Manual (2d ed. 1989)). In general, sequences encoding functional viral reaper proteins that hybridize to the nucleotide sequences disclosed herein will have at least 30% sequence similarity, 50% sequence similarity, 75% sequence similarity, and even 95% sequence similarity or more with the nucleotide sequences encoding viral reaper proteins disclosed herein.

Throughout the present specification and the accompanying claims the words “comprise” and “include” and variations such as “comprises”, “comprising”, “includes” and “including” are to be interpreted inclusively. That is, these words are intended to convey the possible inclusion of other elements or integers not specifically recited, where the context allows.

As referred to above, the present invention relates to methods of using isolated viral reaper proteins or isolated nucleotide molecules encoding viral reaper proteins. In the context of this invention the term “isolated” is intended to convey that the protein is not in its native state, insofar as it has been purified at least to some extent or has been synthetically produced, for example by recombinant methods. The term “isolated” therefore includes the possibility of the protein being in combination with other biological or non-biological material, such as cells, suspensions of cells or cell fragments, proteins, peptides, expression vectors, organic or inorganic solvents, or other materials where appropriate, but excludes the situation where the protein or nucleic acid molecule is in a state as found in nature.

As used herein, the term “viral reaper protein” comprises proteins having an amino acid sequence identical to that of a protein naturally expressed by a virus, and having the ability to induce caspase activation in a vertebrate cell. One method of assaying a protein for the ability to induce caspase activation in a vertebrate cell (Xenopus oocytes) is provided in the Examples section herein.

Routine methods, as further explained in the subsequent experimental section, can be employed to purify and/or synthesize the proteins according to the invention. Such methods are well understood by persons skilled in the art, and include techniques such as those disclosed in Sambrook J., Fritsch E. F. and Maniatis T., Molecular Cloning: a Laboratory Manual; 2^(nd) Edition; CSH Laboratory Press (1989), the disclosure of which is included herein in its entirety by way of reference.

The term “variant” as used herein refers to peptides or proteins which retain the same essential characteristics (functional and structural) of the viral Reaper proteins for which sequence information is provided herein; such variants are intended to be included within the scope of the invention. For example, other peptides or proteins with greater than about 50%, 55%, 60% or 65%, preferably at least 75% and particularly preferably at least 80%, 90% or 95% sequence similarity with the sequences provided, are considered as variants of the proteins. Such variants may include the deletion, modification or addition of single amino acids or groups of amino acids within the protein sequence, as long as the peptide maintains the basic biological functionality of a viral Reaper protein. This biological functionality can be assessed by one skilled in the art using methods that are known in the art.

The term “protein” as used herein is also intended to include within its meaning shorter peptide or polypeptide sequences as well as complete proteins. For example therefore a peptide of only perhaps 15 amino acids in length is considered to fall within the scope of the invention as long as it demonstrates the basic biological functionality of a viral Reaper protein as described herein. In particular, but not exclusively, this aspect of the invention encompasses the situation when the protein is a fragment of the complete protein sequence and may represent a ligand binding region.

The invention also includes methods of using isolated nucleotide sequences that encode viral Reaper proteins or variants thereof, as well as isolated nucleotide sequences which are complementary thereto. The nucleotide sequence may be RNA or DNA including genomic DNA, synthetic DNA or cDNA. Preferably the nucleotide sequence is a DNA sequence and most preferably, a cDNA sequence. Nucleotide sequence information is provided herein for certain viral reapers. Such nucleotides can be isolated from virally infected cells or synthesised according to methods well known in the art, as described by way of example in Sambrook J, Fritsch E. F. and Maniatis T; Molecular Cloning: a Laboratory Manual; 2^(nd) Edition; CSH Laboratory Press (1989), the disclosure of which is included herein in its entirety by reference. The nucleotide molecules according to the invention have utility in production of the proteins according to the invention, which may take place in vitro, in vivo or ex vivo. The nucleotides may be involved in recombinant protein synthesis or indeed as therapeutic agents in their own right, utilised in gene therapy techniques. Nucleotides complementary to those encoding viral Reaper proteins of the present invention, or antisense sequences, may also be used in therapy, such as in strategies for down regulation of expression of the proteins of the invention.

The present invention also includes methods of using expression vectors that comprise nucleotide sequences encoding viral Reaper proteins or variants thereof. Such expression vectors are routinely constructed in the art of molecular biology and may for example involve the use of plasmid DNA and appropriate initiators, promoters, enhancers and other elements, such as for example polyadenylation signals which may be necessary, and which are positioned in the correct orientation, in order to allow for protein expression. Suitable vectors would be apparent to persons skilled in the art. By way of further example in this regard we refer to Sambrook J, Fritsch E. F. and Maniatis T; Molecular Cloning: a Laboratory Manual; 2^(nd) Edition; CSH Laboratory Press (1989), the disclosure of which is included herein in its entirety.

The invention also includes methods of using cell lines that have been modified to express viral reaper proteins. Such cell lines include transient, or preferably stable higher eukaryotic cell lines, such as vertebrate cells, mammalian cells or insect cells; lower eukaryotic cells, such as yeast; or prokaryotic cells such as bacterial cells. Preferred are bacterial, insect and vertebrate cells. As used herein, cells that have been “modified” to express viral reaper proteins are those that contain isolated nucleic acid molecules coding for a viral reaper protein, and excludes cells infected with a virus expressing viral reaper protein from a non-isolated nucleic acid (e.g., a naturally occurring virus).

According to another aspect, the present invention also relates to antibodies (either polyclonal or preferably monoclonal antibodies) which have been raised by standard techniques and are specific for the proteins or variants thereof according to the invention. Such antibodies could for example, be useful in purification, isolation or screening involving immuno precipitation techniques and may be used as tools to further elucidate the protein function, or indeed as therapeutic agents in their own right. Antibodies may also be raised against specific epitopes of the proteins according to the invention.

A further aspect of the present invention is the use of the proteins according to the invention in screening methods designed to identify those compounds that act as ligands for viral Reaper proteins, and/or that modulate viral Reaper protein activity. In general terms, such screening methods will involve contacting the protein concerned, or cell modified to express the protein concerned, with a test compound and then detecting any enhancement or inhibition of protein activity that results (compared to the activity that would occur in the absence of the test compound). The present invention also includes within its scope those compounds that are identified as possessing useful viral Reaper protein modulation activity, by the screening methods referred to above, and use of such compounds. The screening methods comprehended by the invention are generally well known to persons skilled in the art.

Another aspect of the present invention is the use of compounds that have been identified by screening techniques referred to above, or the use of an isolated viral reaper protein, in the treatment or prophylaxis of disorders which are responsive to modulation of viral Reaper protein activity, in a subject in need of such treatment. Preferably such subjects are vertebrates, and more preferably, mammals. The term “modulation”, as used herein, refers to both agonism (enhancement) and antagonism (inhibition) of an activity. Thus modulation may consist of an increase (or a decrease or time delay) in caspase activation or cellular apoptosis, in response to administration of a viral reaper protein (or a compound identified by the screening methods described herein). The change in activity (increase or decrease) is compared to that which would occur in the absence of the added viral reaper protein (or compound). Such increase (or decrease) may be measured by any suitable method as is known to those skilled in the art, e.g., detecting caspase activation over time or counting the number of apoptotic cells in a population over a fixed time period. The modulation activity may be due to direct binding of a compound to the viral reaper protein, or due to the effects of the compound on a downstream element of the apoptotic process that is modulated by the viral Reaper protein. Disorders that are responsive to modulation of cellular apoptosis are those in which the signs, symptoms and/or pathological changes associated with the disorder can be diminished or improved by altering (increasing, decreasing or delaying) cellular apoptosis.

Methods of screening compounds comprise contacting a viral reaper protein with a test compound, or administering a test compound to a cell that contains or expresses a viral reaper protein. By contacting it is meant that the test compound and viral reaper protein are in such proximity that they are able to biologically interact. Administration of a compound to a cell refers to the placement of the compound within the cell interior, either by direct administration or by cellular uptake.

A particular method of screening a compound to determine whether the compound enhances or inhibits caspase activation utilizes vertebrate cell extracts (cell-free preparations) which are known to exhibit detectable caspase activation when functional viral reaper is added to the cell extract. As used herein, an increase in (or enhancement of) caspase activation includes an increase in total caspase activity, a faster rate of caspase activity, and/or a decreased time until caspase activity is detected, as well as other measures that will be apparent to those skilled in the art. As used herein, a decrease in (or inhibition of) caspase activation includes a decrease in total caspase activity, a slowed rate of caspase activity, and/or an increase in the time until caspase activity is first detected; as well as other measures that will be apparent to those skilled in the art. Other indicators of activation of the apoptotic pathway are known in the art, e.g., mitochondrial cytochrome c release, fragmentation of nuclei added to a cell extract preparation. The change in caspase activation (or other indicators of apoptosis) is compared between preparations that contain the test compound and control preparations that do not; however, such comparisons need not be a side-by-side comparison, where a control has previously been tested and has provided data for comparison.

As used herein, a compound with “viral reaper modulating activity” is one that is capable of enhancing or inhibiting viral reaper induced apoptosis or caspase activation. As used herein, apoptosis induced by a viral reaper protein is that caused by activation of the apoptotic pathway by the viral reaper.

Some specific examples of disorders that may be treated or prevented by administration of compounds identified in the screening techniques according to the present invention are viral infections and disorders of apoptosis (such as cancer and neoplastic growths). Mention of such disorders is by way of example only, and is not intended to be limiting on the scope of the invention as described.

The compounds identified according to the screening methods outlined above may be formulated with standard pharmaceutically acceptable carriers and/or excipients as is routine in the pharmaceutical art, and as fully described in Remmington's Pharmaceutical Sciences, Mack Publishing Company, Easton, Pa., 17th Ed, 1985, the disclosure of which is included herein in its entirety by way of reference.

The compounds may be administered via enteral or parenteral routes such as via oral, buccal, anal, pulmonary, intravenous, intraarterial, intramuscular, intraperitoneal, topical or other appropriate administration routes. Appropriate administration routes, effective amounts, and dosing regimes may be determined by one skilled in the art using methods known in the art, e.g., dosage/response studies.

The present invention will now be further described by way of example.

EXAMPLES Example 1 Identification of Viral Reaper Proteins

Using Advanced Blast, Psi Blast, Edit Seq and Meg Align programs, 15 nonstructural viral proteins (or the in silico translated viral DNA for these proteins) were unexpectedly found to have sequence similarity to the Drosophila melanogaster Reaper protein.

The 15 viral proteins (or in silico translated DNAs) investigated were the non-structural proteins (NSs) of San Angelo virus (NSs) (SEQ ID NO:3); Snow Shoe Hare virus (SEQ ID NO:4); La Crosse virus (SEQ ID NO:5), California encephalitis virus (SEQ ID NO:6), Jerry Slough virus (SEQ ID NO:7), Jamestown Canyon virus (SEQ ID NO:8), Keystone virus (SEQ ID NO:9), Melao virus (SEQ ID NO:10), Trivittatus virus (SEQ ID NO:11), Morro Bay virus (SEQ ID NO:12), Inkoo virus (SEQ ID NO:13), Serra do Navio virus (SEQ ID NO:14), South River virus (SEQ ID NO:15), Lumbo virus (SEQ ID NO:16), and Tahyna virus (SEQ ID NO:17). The amino acid sequences of these proteins were compared to that of the D. melanogaster Reaper protein (SEQ ID NO:1) and a portion of the D. melanogaster Grim protein (SEQ ID NO:18) Results are shown in FIG. 1.

It was found that 59 amino acids of the 65 amino acid drosophila reaper protein aligned with 61 amino acids of the ˜92 amino acid viral reaper protein (or in silico translated DNA) with 58% similarity and 29% identity. These points of alignment therefore provide for a consensus reaper sequence cross-species.

A majority sequence was prepared (SEQ ID NO:2).

Example 2 Function of Viral Reaper Proteins

Viral reaper activity is detected utilizing extracts prepared from Xenopus eggs as described in Thress, et al, 1998, The EMBO Journal 17:6135-6143. Briefly, an egg extract prepared as described, is treated with 10 to 1000 nanograms of viral reaper protein or a glutathione-S transferase (GST) fusion protein with viral reaper. Control extracts (without viral reaper) are also prepared. After incubation of the mixture, caspase enzyme activity is measured with the substrate DEVD-pNA by following the increase in absorbance at 405 nanometers. Proteins such as reaper that are apoptotic activators cause an acceleration of the production of caspase activity (compared to that seen in controls).

The presence of apoptotic inhibitors slows or reduces caspase activation in extracts where reaper is incubated with the extract (compared to extracts incubated with reaper that do not contain the apoptotic inhibitor).

Ectopic expression of Drosophila Reaper has also been shown to induce caspase activation and apoptosis in mammalian cells such as human MCF7 breast carcinoma cells (McCarthy & Dixit, J. Biol. Chem. 273:24009 (1998)).

Example 3 Screening for Compounds That Exhibit Viral Reaper Modulating Activity

A cell culture of cells susceptible to viral Reaper-induced effects is established. The viral Reaper protein is administered to the cells (e.g., via transfection with a suitable plasmid and optionally a reporter protein such as B-galactosidase; or by direct administration of the viral reaper protein to the cell). A test compound is also administered to a test population of the cells. Administration of the test compound may occur prior to, concurrently with, or after administration of the viral Reaper protein. The effect of administration of the test compound on apoptosis of cells is compared to a control population of cells that did not receive the test compound. Significant differences in apoptosis (and/or caspase activation or other indicators of apoptosis) between the test and control cells indicates that the test compound modulates viral reaper protein activity.

Alternatively, extracts prepared from Xenopus eggs are used as described herein to test compounds for viral reaper-modulating effects. The test compound is included in an assay as described herein, and caspase activity in cells receiving the test compound is compared to control cells that do not receive the test compound. Significant differences in caspase activity production between the test and control extracts indicates that the test compound modulates viral reaper protein activity.

Example 4 Binding of Drosophila and Viral Reaper to Scythe

Glutathione S-transferase, Drosophila reaper, and two viral reaper proteins were examined to detect the ability to bind to scythe protein. It has previously been shown that drosophila reaper binds to Xenopus scythe protein to induce apoptosis in Xenopus oocytes. Scythe has been indicated as an apoptotic regulator that is an essential component in reaper-induced apoptosis; immunodepletion of scythe from Xenopus egg extracts prevents reaper-induced apoptosis without affecting apoptosis triggered by activated caspase. (Thress et al., EMBO J 17:6135-43 (1998); Evans et al, EMBO J 16:7372-81 (1997); Thress et al., EMBO J 18:5486 (1999)).

Glutathione S-transferase (GST), a Drosophila Reaper-GST construct (RPR), San Angelo virus reaper—GST construct (SA), and California Encephalitis virus reaper—GST construct (CE) were produced in BL21 bacterial strains (using standard techniques as are known in the art) and purified using glutathione sepharose beads. Two preparations of GST prepared by two different individuals were utilized as controls (GST1 and GST2); two preparations of Drosophila reaper prepared by two individuals were also used (RPR1 and RPR2). The Xenopus crude egg extract was prepared as described in Evans et al., EMBO J, 16:7372 (1997) and Thress et al., EMBO J, 17:6135 (1998).

The beads were incubated in Xenopus crude egg extract for an hour. The beads were then washed several times in egg lysis buffer (ELB; 250 mM sucrose, 2.5 mM MgCl2, 1.0 mM dithiothreitol (DTT), 50 mM KCl, 10 mM HEPES), pH 7.4, boiled, and run in an SDS-PAGE gel (using techniques as are well-known in the art) and subjected to Western analysis (using techniques that are well known in the art) to detect binding of scythe to the beads. An aliquot of Xenopus crude egg extract (CS) without any reaper or GST was also run on SDS-PAGE gel as a positive control.

As shown in FIG. 2, no binding was seen with either of the two GST preparations. Drosophila reapers (RPR1 and RPR2) bound scythe; the Xenopus crude egg extract (CS), which contains scythe, was included to show the position of scythe. Additionally, both of the viral reapers (SA and CE) showed scythe binding. The reduced intensity of the Western blot corresponding to viral CE reaper may indicate reduced binding to scythe (compared to the other reaper proteins tested) in this assay, as total reaper or viral reaper protein was maintained constant.

Example 5 Activation of Caspase

Caspase activation was measured using three separate preparations of Drosophila Reaper-GST, San Angelo virus reaper-GST (SA), and California Encephalitis virus reaper-GST(CE) (prepared and purified as described above). GST was used as a control.

Cell-free extracts were prepared from Xenopus oocytes as described in Thress et al., EMBO J, 17:6135 (1998), at page 6141. While it is known that these cell-free extracts will spontaneously release mitochondrial cytochrome c and activate endogenous caspases after prolonged incubation at room temperature, it has further been shown that the addition of drosophila Reaper measurably accelerates this process, triggering mitochondrial cytochrome c release, caspase activation, and fragmentation of added nuclei. (Newmeyer et al., Cell 79:353 (1994); Evans et al., EMBO J. 16:7372 (1997)).

Briefly to assess the ability of a reaper or viral reaper protein to induce caspase release, and thus by inference induce apoptosis, 10 ul of GST-reaper or GST-viral reaper protein (released from GST beads with glutathione under standard conditions) at ˜0.5 to 1 mg/ml was mixed with 100 ul Xenopus oocyte extract. This mixture was incubated for up to 7 hr and assayed for caspase activation a specific times. To measure the caspase activity in the incubation mixtures, 3 μl of each incubation sample were mixed and incubated with 90 μl of assay buffer (50 mM HEPES pH 7.5, 100 mM NaCl, 0.1% CHAPS, 10 mM DTT, 1 mM EDTA, 10% glycerol) and the colorimetric substrate Ac-DEVD-pNA (final concentration 200 μM) [BioMol Caspase-3 assay system; BioMol Research Laboratories Inc., Plymouth Meeting, Pa.] at 37° C. At various time points, absorbance was measured at 405 nm; the measure of absorbance is directly proportional to caspase activation.

As shown by FIG. 3 (Y-axis=absorbance at 405 nm; X-axis=time (in hours), the GST control did not result in activation of caspase, while each of the three Drosophila reaper preparations activated caspase, although the time at which activation was first detected varied among the reaper preparations. Both of the viral reaper preparations resulted in caspase activation. The SA virus reaper activated caspase over a time course similar to that of the Reaper ⅘ preparation in this assay. The CE virus reaper resulted in initial caspase activation at the 6-7 hour timepoint, however, the experiment did not extend beyond this time point. 

1. A method of screening a compound to determine whether the compound affects caspase activation induced by a viral reaper protein, said method comprising: a) obtaining a vertebrate cell extract in which the addition of isolated viral reaper protein induces detectable caspase activation; b) adding isolated viral reaper protein having at least 50% sequence similarity to SEQ ID NO:2 and capable of inducing caspase activation in a vertebrate cell, and a test compound, to said vertebrate cell extract; c) measuring caspase activation; and d) comparing caspase activation that occurs in the presence of the test compound to that which would be expected in the absence of the test compound; where a decrease in caspase activation compared to that which would be expected in the absence of the test compound indicates that said compound inhibits viral reaper-induced caspase activation, and an increase in caspase activation compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced caspase activation.
 2. A method of screening a compound to determine whether the compound affects caspase activation induced by a viral reaper protein, said method comprising: a) obtaining a vertebrate cell extract in which the addition of isolated viral reaper protein induces detectable caspase activation; b) adding isolated viral reaper protein and a test compound to said vertebrate cell extract, where said isolated viral reaper protein comprises an amino acid sequence selected from SEQ ID NOs: 2-17; c) measuring caspase activation; and d) comparing caspase activation that occurs in the presence of the test compound to that which would be expected in the absence of the test compound; where a decrease in caspase activation compared to that which would be expected in the absence of the test compound indicates that said compound inhibits viral reaper-induced caspase activation, and an increase in caspase activation compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced caspase activation.
 3. A method of screening a compound to determine whether the compound affects caspase activation induced by a viral reaper protein, said method comprising: a) obtaining a vertebrate cell extract in which the addition of isolated viral reaper protein induces detectable caspase activation; b) adding isolated viral reaper protein and a test compound to said vertebrate cell extract, where said isolated viral reaper protein is a non-structural protein (NSs) encoded by the viral small RNA from a virus of the Family Bunyaviridae; c) measuring caspase activation; and d) comparing caspase activation that occurs in the presence of the test compound to that which would be expected in the absence of the test compound; where a decrease in caspase activation compared to that which would be expected in the absence of the test compound indicates that said compound inhibits viral reaper-induced caspase activation, and an increase in caspase activation compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced caspase activation.
 4. A method according to claim 1 where said vertebrate cell extract is obtained from Xenopus oocytea.
 5. A method of screening a compound to determine whether the compound affects apoptosis induced by a viral reaper protein, said method comprising: a) obtaining a population of cells, the cells of a type in which the addition of isolated viral reaper protein induces apoptosis; b) administering isolated viral reaper protein having at least 75% sequence similarity to SEQ ID NO:2 and capable of inducing caspase activation in a vertebrate cell, and a test compound, to said cells; c) measuring apoptosis that occurs in said cell population; and d) comparing apoptosis that occurs in the presence of the test compound to that which would be expected in the absence of the test compound; where a decrease in apoptosis indicates that said compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis a compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced apoptosis.
 6. A method according to claim 5 wherein said population of cells consists of vertebrate cells.
 7. A method of screening a compound to determine whether the compound affects apoptosis induced by a viral reaper protein, said method comprising: a) obtaining a population of cells, the cells of a type in which the addition of isolated viral reaper protein induces apoptosis; b) administering isolated viral reaper protein and a test compound to said cells where said isolated viral reaper protein comprises an amino acid sequence selected from SEQ ID Nos: 2-7; c) measuring apoptosis that occurs in said cell population; and d) comparing apoptosis that occurs in the presence of the test compound to that which would be expected in the absence of the test compound; where a decrease in apoptosis indicates that said compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced apoptosis.
 8. A method of screening a compound to determine whether the compound affects apoptosis induced by a viral reaper protein, said method comprising: a) obtaining a population of cells, the cells of a type in which the addition of isolated viral reaper protein induces apoptosis; b) administering isolated viral reaper protein and a test compound to said cells where said isolated viral reaper protein is a non-structural protein (NSs) encoded by the viral small RNA from a vinis of the Family Bunyaviridae; c) measuring apoptosis that occurs in said cell population; and d) comparing apoptosis that occurs in the presence of the test compound to that which would be be expected in the absence of the test compound; where a decrease in apoptosis indicates that said compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis compared to that which would be expected in the absence of the test compound indicates that said test compound enhances viral reaper-induced apoptosis.
 9. A method according to claim 5 wherein said isolated viral reaper protein is administered by transfecting cells with a nucleotide molecule encoding the viral reaper protein.
 10. A method according to claim 5 where apoptosis is measured by a criterion selected from the group consisting of caspase activation, cell death, or cellular DNA degradation over time.
 11. A method of screening a compound for viral reaper modulating activity, said method comprising: (a) obtaining a population of cells modified to express an isolated viral reaper protein having at least 75% sequence similarity to SEQ ID NO:2, and capable of inducing caspase activation in a vertebrate cell; (b) administering to a test population of said cells a test compound; and (c) comparing apoptosis occurring in said test population of cells to that which would be expected in a population of cells that did not receive said test compound; where a reduction in apoptosis indicates that said test compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis indicates said test compound enhances viral-reaper induced apoptosis.
 12. A method according to claim 11 where said population of cells consists of insect cells.
 13. A method according to claim 11 where said population of cells consists of vertebrate cells.
 14. A method according to claim 11 where apoptosis is measured by a criterion selected from caspase activation, cell death, or cellular DNA degradation over time.
 15. A method of screening a compound for viral reaper modulating activity, said method comprising: (a) obtaining a population of cells modified to express an isolated viral reaper protein, where said isolated viral reaper protein comprises an amino acid sequence selected from SEQ ID NO.: 2-7; (b) administering to a test population of said cells a test compound; and (c) comparing apoptosis occurring in said test population of cells to that which would be expected in a population of cells that did not receive said test compound; where a reduction in apoptosis indicates that said test compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis indicates said test compound enhances viral-reaper induced apoptosis.
 16. A method of screening a compound for viral reaper modulating activity, said method comprising: (a) obtaining a population of cells modified to express an isolated viral reaper protein, where said isolated viral reaper protein is a non-structural protein (NSs) encoded by the viral small RNA from a virus of the Family Bunyaviridae; (b) administering to a test population of said cells a test compound; and (c) comparing apoptosis occurring in said test population of cells to that which would be expected in a population of cells that did not receive said test compound; where a reduction in apoptosis indicates that said test compound inhibits viral reaper-induced apoptosis, and an increase in apoptosis indicates said test compound enhances viral-reaper induced apoptosis.
 17. A method of inducing apoptosis in a vertebrate cell by administering an isolated viral reaper protein to said cell, in an amount sufficient to enhance apoptosis over that which would be seen in the absence of viral reaper protein, where said viral reaper protein is a protein having at least 75% sequence similarity to SEQ ID NO:2, and is capable of inducing caspase activation in a vertebrate cell.
 18. A method according to claim 17 wherein said vertebrate cell is a mammalian cell.
 19. A method according to claim 17 where administration of the viral reaper protein is by transfection with an isolated nucleic acid molecule encoding said viral reaper protein.
 20. A method according to claim 17 where an expression vector containing an isolated nucleotide sequence encoding said viral reaper protein is administered to said cell.
 21. A method of inducing apoptosis in a vertebrate cell by administering an isolated viral reaper protein to said cell, in an amount sufficient to enhance apoptosis over that which would be seen in the absence of viral reaper protein, where said isolated viral reaper protein is a non-structural protein (NSs) encoded by the viral small RNA from a virus of the Family Bunyaviridae. 